what other materials do people use for sketches and renderings besides pencil, pen and markers or computer? i've heard of water color or ink washes. what are some other methods? any good "how to" books, websites or examples?

Seriously though,
you have touched upon a number,
I dont know what types of drawing you are rendering but I usually find it helpful to go to a big art store, or craft store; walk down the isles, pick up anything you havent used to render or draw, and, think about how you could make it work, or, buy it bring it home, and play with it. Have you tried photographic manipulations? Also there are a number of colour application processes, involving films, etc.

For awhile I was on the whole charcoal on newsprint kind of thing, and then on the old school canson (which you can simulate digitally pretty easy), but really you just need to try stuff. The trick is to keep it appropriate. Remember the function of a sketch is to visually communicate something and the worst thing is when a technique gets in the way of that communication:

Some newsprint/canson loose sketches:

I've been drawing a lot on big post it notes lately (an idea I got from another designer here) because you can move them around take em down ect.